Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$239.59	6.592%	$255.3838	$255.38	$255.40	$255.40
Purchase #2	$55.88	10.144%	$61.5485	$61.55	$61.55	$61.50
Purchase #3	$203.97	6.663%	$217.5605	$217.56	$217.55	$217.60
Purchase #4	$12.28	6.398%	$13.0657	$13.07	$13.05	$13.10
Purchase #5	$162.48	6.582%	$173.1744	$173.17	$173.15	$173.20
Purchase #6	$105.74	8.115%	$114.3208	$114.32	$114.30	$114.30
Purchase #7	$196.42	12.143%	$220.2713	$220.27	$220.25	$220.30
7 purchase totals =	$976.36		$1,055.3250	$1,055.32	$1,055.25	$1,055.40